Use any KDE application source as an example, or one of the KDE application templated of KDevelop.
Basically all user visible strings are marked with i18n() instead of tr(), the makefile can extract and merge the messages into a .po file, which can be copied and translated.
A tool then generates translation catalogue files (.mo)
Description of the translation process for example on the KDE translators web site
http://i18n.kde.org/
(especially for setups with non-latin languages like Asian languages it might be helpful to contact the KDE translation team for your own language, they might have some tips for you)
The base for this is the GNU gettext framework, used by most free software project that need internationalized output.
Anyway, if your other KDE applications appear correctly, do they so if started the same way as your application?
I mean if you start your application from commandline for testing, does a KDE application started from commandline hav correct translations?
Cheers,
_